I am looking to add a longer lens to my current zoom (a Tamron 17-50) for my Nikon D300 (but I believe this question is relevant across aps-c lens manufacturers).

There is just one currently in production — the Pentax 50-135 f/2.8 (which is Pentax mount only).

What is the reason behind this? Is there a physical reason why making a smaller DX alternative to a 70-200 is not be possible? I have seen it mentioned that "beyond 100mm the advantage in making dx lenses is gone", but not sure if this is folklore or a genuine restriction.

2 Answers
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Actually the same 50-135 f/2.8 lens was sold by Tokina for other mounts, but it was discontinued in 2009.

I'd say the primary reason is that there's no significant savings between making a telephoto lens just for APS-C or one that's also good for full frame. In fast telephoto lenses, the majority of glass goes towards achieving the big aperture needed, the smaller image circle won't introduce very significant differences.

Another reason is that since a fast telephoto zoom is an expensive lens, many of the buyers are already considering getting a full-frame body in the future, and would dismiss an APS-C lens. This leaves a smaller pool of potential buyers, meaning less potential profit. Pentax doesn't have to worry about it, since they don't have a full frame body, nor have they announced any plan of making one.

Hi Imre, thats pretty much what i thought. But i dont understand where there are so many normal fast zooms of 24-70 equivalent, but not one fast zoom offering the 70-200 equivalent (apart from the discontinued sigma and tokina). the dx equivalent of a 70-200 would be much smaller / cheaper, but i guess seeing both tokina and sigma leave this niche, it is not very profitable at all. Cheers
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rapscalliJan 29 '12 at 23:40

ps the linked question you gave gave an answer that explained part of the similarity in build. the front element is a fixed size for a given focal length / aperture, regardless of sensor size.
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rapscalliJan 29 '12 at 23:41

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@rapscalli For wider angles, you need glass to build up the wide angle of view and reduce aberrations on peripheral areas. The angle is smaller on a crop sensor, so the savings in weight and cost are more significant.
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ImreJan 30 '12 at 6:09

I have that Tokina. No stabilization but great lens otherwise. Shame sigma discontinued theirs: a 70-200 on APS-C just feels a tad too long and the usual ~20-~200 trans-standards are too dim, not mentioning other optical considerations.
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BerzemusJan 31 '12 at 12:55

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There are significant savings to be made by making a fast wideangle lens APS-C only, but very little in making a telephoto lens APS-C only, so they don't bother.
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Matt GrumOct 31 '13 at 15:52

I wonder the same question as the OP. Even the one that is being produced - Sigma 50-150mm - is really big and chunky, not much smaller than full-frame 70-200mm f/2.8. I can't see any benefit to be gained from a smaller sensor and shorter focal length in that product.

Hi anon, i believe sigma used the 70-200 body for the new 50-150, probably to save costs. One possible side effect of using the larger body is its very, very high performance.
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rapscalliNov 5 '13 at 8:22